The present invention relates to an axial flow fan, and more particularly to an improved printed circuit board and fan housing, and improved blades comprising a new airfoil family having the advantages of decreasing the axial width of the axial flow fan while maintaining its performance parameters and design constraints. The axial flow fan of the present invention is especially suitable for use in cooling electronic components.
A conventional axial flow fan is generally composed of a driving motor, a cylindrical central hub section, a plurality of blades, and a housing for encasing the fan. Each of the blades extends radially outward from the central hub section of the fan. A motor shaft of the driving motor is attached to the hub section at a central aperture and thus the hub section may be rotated by the driving motor via the motor shaft. In such an arrangement, the hub section together with the blades rotate about an axis of the outer casing in order to force air flow from an inlet area to an outlet area of the fan. The motor rotates the blades of the fan via the motor shaft so as to make the blades generate a lifting force which is, in a form, the fan pressure and air flow.
Axial flow fans such as Model No. 5920 produced by IMC Magnetics Corporation, the assignee of the present application, are known which utilize a unipolar winding employing a four pole motor where only two of the windings are ON at a time. These fans employ circuitry including circuit elements of a substantial size, such as an inductor to reduce the starting current, transistors large enough to handle the power levels, and large clamping diodes needed to protect the transistors. Such axial flow fans cannot handle input voltages in the range of 57V-64V, are limited to a maximum input voltage of about 56V, and are more typically operated at an input voltage of about 48V.
Model No. 5920 measures two inches in axial width due to both the large size of the diodes, inductors, and transistors used, as well as the number of turns required for a unipolar winding. Furthermore, the axial width of Model No. 5920 is attributed to its 5 blades wherein each blade is characterized by a symmetrical cross-section approximately described as curved flat plates. As such, these blades are not aerodynamically efficient and thus require a larger chord length to meet the performance requirements forcing the dimensions of Model No. 5920 to a two inch axial width.
With the continual increase in the density and load-carrying capability of electronic components on circuit boards, and the consequential increase in heating problems resulting therefrom, axial flow fans are increasingly being used in an effort to combat such heating problems. During the design of such axial flow fans, it is important to make them as small and as cost-effective as possible. In particular, it is important to reduce the axial width of such a fan as much as possible. For example, the two inches axial width of Model No. 5920 is wider than optimal for use as an axial flow fan for cooling electronic components. Thus, it is desirable to reduce its size while maintaining its performance parameters and design constraints.
One method to reduce the axial width of such a fan is to eliminate large electronic components and reduce the size of other components while maintaining performance parameters and design constraints. Furthermore, the housing of the axial flow fan may also be utilized to reduce the axial width.
In addition, in order to reduce the axial width of an axial flow fan, it is desirable to utilize narrow chord blades. However, the use of such narrow chord blades results in decreased performance, particularly a decrease in the fan pressure and air flow. These decreases in performance must be offset by varying the design parameters. It is known that, among other factors, the chord length, camber angle, stagger angle, and the cross-sectional shape of the blades are possible factors affecting the performance of the fan. In addition, it is known that by varying the work distribution along a blade""s span, the chord length may be varied along the blade span while maintaining performance parameters.
However, no invention in the prior art discloses a combination of these and other factors to formulate a blade which delivers the desired performance while reducing the axial width to that of the present invention.
For example, in theory, the larger the camber angle, the greater the lift force under a constant angle of attack. However, if the camber angle is too large the blade may stall resulting in a decrease in performance and an increase in noise signature. Consequently, the camber angle must be designed to the proper value.
By way of a further example, a decrease in the work distribution at a radial location will allow for a decrease in chord length with a resultant decrease in velocity exiting the blade at that radial location. Thus, it is desirable to minimize the work distribution at the hub section (root of the blade), since this affects axial width, and to maximize the work distribution at the tip of the blade to deliver the greatest blade exit velocity at the tip. Such an approach was disclosed in U.S. Pat. No. 5,320,493. However, this approach may lead to an intolerable increase in the noise signature of the fan due to the increase in tip velocity exiting the blade as well as an increase in turbulent air exiting the tip of the blades. Thus, it is desirable to locate the maximum work distribution at some favorable location between the root portion and the tip portion.
Furthermore, the cross-sectional shape of the blade affects its velocity distribution. Circular arc profiles, such as NACA series 65 airfoils, exhibit a velocity profile which results in a rapid decrease in the velocity along the suction surface at the trailing edge of the blade. Such a large deceleration gradient results in a more unstable boundary layer, promoting boundary layer separation and hence resulting in loss of lift and greater turbulent air exiting the blade. Thus, the velocity profile of the cross-sectional airfoil must be designed so that a favorable velocity profile is achieved.
Various prior U.S. patents had been developed in this field. For example, U.S. Pat. No. 4,971,520, U.S. Pat. No. 4,569,631, U.S. Pat. No. 5,244,347, U.S. Pat. No. 5,326,225, U.S. Pat. No. 5,513,951, U.S. Pat. No. 5,320,493, U.S. Pat. No. 5,181,830, U.S. Pat. No. 5,273,400, No. 2,811,303, and U.S. Pat. No. 5,730,483 disclose axial flow fans. However, the fans disclosed in these patents have not effectively combined the above parameters to overcome the problems described above. In particular no invention discloses a family of airfoil profiles or a blade which delivers the performance of the present invention while reducing the axial width of the fan.
Accordingly, it is an object of this invention to provide an axial flow fan with reduced axial width while maintaining performance parameters and design constraints.
An additional object is to provide an axial flow fan with reduced axial width by eliminating large electronic circuit components.
It is yet another object of the invention to provide an axial flow fan that is capable of operating from a starting voltage in the range of about 28V-64V.
It is a further object of the invention to provide an axial flow fan with reduced axial width by employing the housing as a heat sink.
It is still a further object of the invention to provide an axial flow fan with reduced axial width by employing a voltage regulator IC.
It is an additional object of the invention to provide an axial flow fan with reduced axial width by employing a bipolar winding motor.
It is an additional object of the invention to provide a blade incorporating a family of airfoil sections capable of reducing the axial width of an axial flow fan while maintaining performance parameters and design constraints.
It is yet another object of the invention to provide a blade incorporating a family of airfoil sections which allow for the reduction of the axial width of an axial fan while locating the maximum work distribution between the root portion and the tip portion of the blade.
It is yet another object of the invention to provide a blade incorporating a family of airfoil sections which allow for the reduction of the axial width of an axial fan while maintaining a favorable velocity profile over the suction side of the blade.
These and other objects are realized by a stator comprising a core and at least one winding, and a printed circuit board having circuitry for operating the motor, the printed circuit board secured to the stator and electrically connected to the at least one winding of the stator. The circuitry includes a voltage regulator.
Also provided is an axial flow fan comprising: a motor comprising a magnet, a yoke, and a stator assembly. The stator assembly includes a core, at least one winding, and a printed circuit board secured to the core and electrically connected to the one winding. The axial flow fan further comprises an impeller and a fan housing, wherein the housing also functions as a heat sink.
These and other objects are further realized by: a blade for an impeller having a root portion, a tip portion, a leading edge, a trailing edge, the blade having a cross-sectional shape, taken anywhere along a radius of the blade, characterized by a maximum thickness located substantially constantly between about 19% chord to about 20% chord and a maximum camber located substantially constantly between about 45% chord to about 46% chord; an impeller consisting of at least thirteen of such circumferentially spaced, radially extending blades coupled to a circular band at the root portion of the blade; an axial flow fan comprising such an impeller, a driving motor, a yoke section that is rotatable about an axis and driven by the driving motor, and a fan housing that concentrically surrounds such an impeller; and a blade for an impeller having a root portion, a tip portion, a leading edge, a trailing edge, the blade being characterized in plan form wherein the blade is varied from the root portion to the tip portion with a maximum chord located between the root portion and the tip portion, the leading edge and the trailing edge of the blade are convex from the root portion to the tip portion.
As such, the novel circuitry, fan housing, and blade of the invention provide for a reduced axial width of an axial flow fan while maintaining its performance parameters and design constraints. These and other objects, features, and advantages of the present invention will become more apparent in light of the following detailed description and accompanying drawings.